Overview

The ABB RET 521 is a numerical microprocessor‑based protection terminal that provides advanced transformer protection functions in a compact design. It is engineered to safeguard two‑winding and three‑winding transformers, generator‑transformer blocks, and reactors. Moreover, it integrates multiple protective features such as inrush restraint, overexcitation protection, and zero‑sequence current elimination. In addition, the RET 521 supports flexible breaker arrangements without requiring interposing current transformers, making installation and configuration straightforward.

Its design emphasizes operational security and productivity, ensuring that transformers operate safely under varying load conditions. Therefore, it is trusted in both industrial plants and utility substations where continuous reliability is essential.

Technical Data

Typical Applications

• Power transformers in utility substations requiring advanced digital protection.

• Generator‑transformer blocks in power plants for secure operation.

• Industrial reactors and transformer banks in heavy industries such as steel, paper, and chemical processing.

• Widely adopted in retrofit projects to replace older electromechanical relays with modern digital protection.

• Applied in multi‑breaker arrangements where flexible connection options are required.

FAQ

Q1: What is the ABB RET 521 used for?
A1: It protects, controls, and monitors transformers, ensuring safe and reliable operation.

Q2: Can the RET 521 handle multiple transformer types?
A2: Yes, it supports both two‑winding and three‑winding transformer applications.

Q3: What protective functions are included?
A3: It provides inrush restraint, overexcitation restraint, cross‑blocking between phases, and zero‑sequence current elimination.

Q4: Is the RET 521 suitable for retrofit projects?
A4: Yes, it replaces older relay systems and integrates easily into modern digital networks.